During a semiconductor fabrication process, a wafer needs to be transferred between different manufacturing processes, as well as between different regions of the same manufacturing process. A wafer cassette is often used in both the transportation and storage processes. The wafer cassette can provide a clean environment for holding the wafer, and avoid contaminations on the wafer from contamination sources in the manufacturing environment which may have a lower cleanliness level compared to the wafer cassette.
To improve utilization of the wafer cassette, a plurality of wafers are usually stored in one wafer cassette. The wafer cassette has a plurality of card slots. The card slots can divide and support the wafers, thus the bottom of the wafer is suspended and the wafers are placed in an orderly manner in the wafer cassette. When the equipment the manufacturing process fails or needs maintenance, the wafers need to be placed in the wafer cassette by a manual operation.
However, when manually placing the wafers in an existing wafer cassette, the wafers are easily scratched. The disclosed device structures and methods are directed to solve one or more problems set forth above and other problems.